The present invention relates generally to field devices for process measurement and control. Specifically, the invention concerns isolating electronics from environmental effects in a process transmitter.
Field devices cover a broad range of process management devices that measure and control parameters such as pressure, temperature, and flow rate. A process transmitter is a type of field device in communication with a transducer, for example a sensor or an actuator, and also in communication with a remote monitoring or control device, such as a computer. The output signal of a sensor, for example, is generally insufficient to communicate effectively with a remote monitoring or control device. The process transmitter bridges the gap by receiving the communication from the sensor, converting the signal to a form more effective for longer distance communication, for example a modulated 4-20 mA current loop signal, or a wireless protocol signal, and transmitting the converted signal over a current loop or through a wireless field device network to the remote monitoring or control device.
Process transmitters often employ a dual-compartment housing. In a typical dual-compartment housing, one compartment contains process transmitter electronics and the other contains a terminal block to provide field connections to the process transmitter electronics for, for example, process control loop wires. Dual-compartment housings are often cylindrical, with the two compartments in a back-to-back arrangement separated by a central wall. Electrical connections between the terminal block and the process transmitter electronics pass through this central wall. The terminal block compartment is accessible from one side and the process electronics compartment is accessible from the other.
Process electronics must be protected from external environmental hazards, such as moisture, dirt, and radio frequency interference (RFI). Failure to adequately isolate the process electronics may cause erroneous signal conversions, communication disruption, and process transmitter failure. The terminal block compartment is occasionally opened in the field, exposing the compartment and components inside to the external environmental hazards. In addition, conduits carrying field connection wiring often connect directly to the terminal block compartment and may carry moisture into the compartment. The terminal block components are not typically sensitive to the effects of the external environmental hazards, but the electrical connections passing through the central wall between the terminal block and the process transmitter electronics can act as a pathway to carry the external environmental hazards into the electronics compartment. Thus, an environmental seal of the electrical connections between the two compartments is necessary to isolate and protect the process transmitter electronics from the external environmental hazards.
Unfortunately, solutions that provide an effective environmental seal in the case of a typical back-to-back cylindrical configuration of the dual-compartment housing are often not suitable for other dual-compartment configurations.